Engines may be configured to operate with a variable number of active or deactivated cylinders to increase fuel economy, while optionally maintaining the overall exhaust mixture air-fuel ratio about stoichiometry. This operation may be referred to as VDE (variable displacement engine) operation. In some examples, a portion of an engine's cylinders may be disabled during selected conditions, where the selected conditions can be defined by parameters such as a speed/load window, as well as various other operating conditions including vehicle speed. A control system may disable selected cylinders through the control of a plurality of cylinder valve deactivators that affect the operation of the cylinder's intake and exhaust valves. By reducing displacement under low torque request situations, the engine is operated at a higher manifold pressure, reducing engine friction due to pumping, and resulting in reduced fuel consumption.
However, a potential issue with variable displacement engines may occur when transitioning between the various displacement modes, for example, when transitioning from a non-VDE (or full-cylinder) mode to a VDE (or reduced cylinder) mode, and vice-versa. As an example, a four cylinder engine that can be operated in three distinct operation modes including a full-cylinder mode, a three-cylinder mode, and a two-cylinder mode may be transitioned between the three modes in response to changes in engine loads. These transitions can significantly affect the manifold pressure, engine airflow, engine torque output, and engine power. In one example, these transitions may produce disturbances in engine torque and may increase noise, vibration, and harshness (NVH) of the engine. One solution to reducing torque disturbances during transitions may be to switch between operating modes at specific timings. However, while timing a transition may lessen torque disturbances, noise and vibrations may continue to be perceived.
The inventors herein have recognized the above issues and identified an approach to at least partially address these issues. In one example approach, a method comprises transitioning an engine with only four cylinders between two-cylinder, three-cylinder, and four-cylinder modes of operation with a sequence of firing events, the sequence including at least two successive firing events separated by at least 120 crank angle degrees, and adjusting one or more active mounts coupled to the engine in response to the transitioning. In this way, vibrations resulting from torque disturbances during engine operation transitions may be reduced.
As an example, a four-cylinder engine may be configured to operate in a two-cylinder VDE mode, a three-cylinder VDE mode, and a four-cylinder (or full-cylinder) mode. As such, three of the four cylinders may be deactivatable. The two-cylinder mode may include activating a first cylinder and a second cylinder while a third cylinder and a fourth cylinder are deactivated. Further, the first cylinder and the second cylinder may be fired at 360 crank angle degree intervals in the two-cylinder mode. The three-cylinder mode of engine operation may include deactivating the first cylinder, and activating the third cylinder and the fourth cylinder. Further, the second cylinder, the third cylinder and the fourth cylinder may be fired at evenly spaced 240 crank angle degree intervals from each other. Finally, the four-cylinder or non-VDE mode may include activating all cylinders and operating with uneven firing intervals. Herein, the first cylinder may be fired 120 crank angle degrees after a firing event in the fourth cylinder, the third cylinder may be fired 120 crank angle degrees after firing the first cylinder, the second cylinder may be fired 240 crank angle degrees after firing the third cylinder, and the fourth cylinder may be fired 240 crank angle (CA) degrees after firing the second cylinder. The engine may also be coupled to a vehicle frame via one or more active mounts.
Transitions between the two-cylinder mode, the three-cylinder mode, and the non-VDE mode may include activating and/or deactivating specific cylinders based on current and eventual engine operating modes. Further, the activation and/or deactivation of cylinders, as well as firing events in the activated and/or deactivated cylinders, may occur in a sequence with intervals that reduces torque disturbances. Further still, one or more active mounts may be activated to counteract vibrations resulting from torque disturbances. As such, the one or more active mounts may provide a distinct input function for each specific transition sequence.
In one example, the engine may be transitioned from two-cylinder mode to four-cylinder mode by activating the third cylinder and the fourth cylinder. A smoother transition may be achieved by activating the third cylinder earlier than the fourth cylinder and timing a transition sequence as follows: activation of the third cylinder followed by a firing event in the second cylinder, firing of the first cylinder 360 CA degrees after the firing event in the second cylinder, activation of the fourth cylinder, firing of the third cylinder 120 CA degrees after the firing event in the first cylinder, firing of the second cylinder 240 CA degrees after firing the third cylinder, and firing of the fourth cylinder 240 CA degrees after firing the second cylinder. Herein, the sequence of five successive firing events includes a firing interval of at least 120 CA degrees between at least two successive firing events. In addition to the above transition sequence, one or more active mounts coupled to the engine may be triggered to provide an input function specific to the above transition. Further, the one or more active mounts may be triggered when valvetrain switching solenoids are activated.
In another example, engine operation may be transitioned from four-cylinder mode to three-cylinder mode by deactivating the first cylinder. The first cylinder may be deactivated following a last firing event in the first cylinder. The third cylinder may be fired 120 CA degrees after the last firing event in the first cylinder followed by a firing event in the second cylinder 240 CA degrees after firing the third cylinder. The fourth cylinder may be fired 240 CA degrees after firing the second cylinder, and the third cylinder may be fired again 240 CA degrees after firing the fourth cylinder. Since the first cylinder has been deactivated, it may not fire between the fourth cylinder and the third cylinder. Thus, the sequence of firing events in the transition may include at least two successive firing events that occur with an interval of 120 CA degrees e.g. interval of 120 CA degrees between the last firing event in the first cylinder and the following firing event in the third cylinder. In addition to transitioning engine operation with the above sequence, one or more active mounts may be actuated to further diminish vibrations.
In this way, engine operation may be transitioned between three available modes to reduce torque disturbances. By scheduling transitions such that firing events during the transition phase occur at specific intervals, a smoother transition with reduced NVH may be attained. Fuel consumption may also be decreased by enabling timely transitions. By actuating one or more active mounts with different input functions in response to each transition sequence, perceptible NVH may be further reduced. Overall, passenger comfort may be improved, and engine operation and drivability may be enhanced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.